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rough idle and surging on very cold mornings

Hi all. I have a 93 525i m50. When the weather started getting very cold I have a very rough idle and surging and a cel indicating an oxygen sensor in the morning. Car seems like its going to stall sometimes at stoplights. When the car warms up the cel dissapears and all is normal. I replaced the o2 sensor with a new bosch unit 7 months ago. I found some splits in the hose connections on the intake boot and replaced with a new one. I also replaced the throttle body gasket because it was easy and cheap. fuel pump is new. I am suspecting a vacuum leak. The oil cap is new as well as the valve cover gasket and asscociated plug gaskets. I am going to spray carb cleaner around the intake gaskets and check for leaks. I already purchased the gaskets. What could it be?